aerospace engineering

aerospace engineering, also called aeronautical engineering, or astronautical engineering,
field of engineering concerned with the design, development, construction, testing, and operation of vehicles operating in the Earth’s atmosphere or in outer space. In 1958 the first definition of aerospace engineering appeared, considering the Earth’s atmosphere and the space above it as a single realm for development of flight vehicles. Today the more encompassing aerospace definition has commonly replaced the terms aeronautical engineering and astronautical engineering.

The design of a flight vehicle demands a knowledge of many engineering disciplines. It is rare that one person takes on the entire task; instead, most companies have design teams specialized in the sciences of aerodynamics, propulsion systems, structural design, materials, avionics, and stability and control systems. No single design can optimize all of these sciences, but rather there exist compromised designs that incorporate the vehicle specifications, available technology, and economic feasibility.

History

Aeronautical engineering

The roots of aeronautical engineering can be traced to the early days of mechanical engineering, to inventors’ concepts, and to the initial studies of aerodynamics, a branch of theoretical physics. The earliest sketches of flight vehicles were drawn by Leonardo da Vinci, who suggested two ideas for sustentation. The first was an ornithopter, a flying machine using flapping wings to imitate the flight of birds. The second idea was an aerial screw, the predecessor of the helicopter. Manned flight was first achieved in 1783, in a hot-air balloon designed by the French brothers Joseph-Michel and Jacques-Étienne Montgolfier. Aerodynamics became a factor in balloon flight when a propulsion system was considered for forward movement. Benjamin Franklin was one of the first to propose such an idea, which led to the development of the dirigible. The power-driven balloon was invented by Henri Gifford, a Frenchman, in 1852. The invention of lighter-than-air vehicles occurred independently of the development of aircraft. The breakthrough in aircraft development came in 1799 when Sir George Cayley, an English baron, drew an airplane incorporating a fixed wing for lift, an empennage (consisting of horizontal and vertical tail surfaces for stability and control), and a separate propulsion system. Because engine development was virtually nonexistent, Cayley turned to gliders, building the first successful one in 1849. Gliding flights established a data base for aerodynamics and aircraft design. Otto Lilienthal, a German scientist, recorded more than 2,000 glides in a five-year period, beginning in 1891. Lilienthal’s work was followed by the American aeronaut Octave Chanute, a friend of the American brothers Orville and Wilbur Wright, the fathers of modern manned flight.

Following the first sustained flight of a heavier-than-air vehicle in 1903, the Wright brothers refined their design, eventually selling airplanes to the U.S. Army. The first major impetus to aircraft development occurred during World War I, when aircraft were designed and constructed for specific military missions, including fighter attack, bombing, and reconnaissance. The end of the war marked the decline of military high-technology aircraft and the rise of civil air transportation. Many advances in the civil sector were due to technologies gained in developing military and racing aircraft. A successful military design that found many civil applications was the U.S. Navy Curtiss NC-4 flying boat, powered by four 400-horsepower V-12 Liberty engines. It was the British, however, who paved the way in civil aviation in 1920 with a 12-passenger Handley-Page transport. Aviation boomed after Charles A. Lindbergh’s solo flight across the Atlantic Ocean in 1927. Advances in metallurgy led to improved strength-to-weight ratios and, coupled with a monocoque design, enabled aircraft to fly farther and faster. Hugo Junkers, a German, built the first all-metal monoplane in 1910, but the design was not accepted until 1933, when the Boeing 247-D entered service. The twin-engine design of the latter established the foundation of modern air transport.

The advent of the turbine-powered airplane dramatically changed the air transportation industry. Germany and Britain were concurrently developing the jet engine, but it was a German Heinkel He 178 that made the first jet flight on Aug. 27, 1939. Even though World War II accelerated the growth of the airplane, the jet aircraft was not introduced into service until 1944, when the British Gloster Meteor became operational, shortly followed by the German Me 262. The first practical American jet was the Lockheed F-80, which entered service in 1945.

Commercial aircraft after World War II continued to use the more economical propeller method of propulsion. The efficiency of the jet engine was increased, and in 1949 the British de Havilland Comet inaugurated commercial jet transport flight. The Comet, however, experienced structural failures that curtailed the service, and it was not until 1958 that the highly successful Boeing 707 jet transport began nonstop transatlantic flights. While civil aircraft designs utilize most new technological advancements, the transport and general aviation configurations have changed only slightly since 1960. Because of escalating fuel and hardware prices, the development of civil aircraft has been dominated by the need for economical operation.

Technological improvements in propulsion, materials, avionics, and stability and controls have enabled aircraft to grow in size, carrying more cargo faster and over longer distances. While aircraft are becoming safer and more efficient, they are also now very complex. Today’s commercial aircraft are among the most sophisticated engineering achievements of the day.

Smaller, more fuel-efficient airliners are being developed. The use of turbine engines in light general aviation and commuter aircraft is being explored, along with more efficient propulsion systems, such as the propfan concept. Using satellite communication signals, onboard microcomputers can provide more accurate vehicle navigation and collision-avoidance systems. Digital electronics coupled with servo mechanisms can increase efficiency by providing active stability augmentation of control systems. New composite materials providing greater weight reduction; inexpensive one-man, lightweight, noncertified aircraft, referred to as ultralights; and alternate fuels such as ethanol, methanol, synthetic fuel from shale deposits and coal, and liquid hydrogen are all being explored. Aircraft designed for vertical and short takeoff and landing, which can land on runways one-tenth the normal length, are being developed. Hybrid vehicles such as the Bell XV-15 tilt-rotor already combine the vertical and hover capabilities of the helicopter with the speed and efficiency of the airplane. Although environmental restrictions and high operating costs have limited the success of the supersonic civil transport, the appeal of reduced traveling time justifies the examination of a second generation of supersonic aircraft.

Aerospace engineering

The use of rocket engines for aircraft propulsion opened a new realm of flight to the aeronautical engineer. Robert H. Goddard, an American, developed, built, and flew the first successful liquid-propellant rocket on March 16, 1926. Goddard proved that flight was possible at speeds greater than the speed of sound and that rockets can work in a vacuum. The major impetus in rocket development came in 1938 when the American James Hart Wyld designed, built, and tested the first U.S. regeneratively cooled liquid rocket engine. In 1947 Wyld’s rocket engine powered the first supersonic research aircraft, the Bell X-1, flown by the U.S. Air Force captain Charles E. Yeager. Supersonic flight offered the aeronautical engineer new challenges in propulsion, structures and materials, high-speed aeroelasticity, and transonic, supersonic, and hypersonic aerodynamics. The experience gained in the X-1 tests led to the development of the X-15 research rocket plane, which flew nearly 200 flights over a nine-year period. The X-15 established an extensive database in transonic and supersonic flight (up to five times the speed of sound) and revealed vital information concerning the upper atmosphere.

The late 1950s and ’60s marked a period of intense growth for astronautical engineering. In 1957 the U.S.S.R. orbited Sputnik I, the world’s first artificial satellite, which triggered a space exploration race with the United States. In 1961 U.S. president John F. Kennedy recommended to Congress to undertake the challenge of “landing a man on the Moon and returning him safely to the Earth” by the end of the 1960s. This commitment was fulfilled on July 20, 1969, when astronauts Neil A. Armstrong and Edwin E. Aldrin, Jr., landed on the Moon.

The 1970s began the decline of the U.S. manned spaceflights. The exploration of the Moon was replaced by unmanned voyages to Jupiter, Saturn, and other planets. The exploitation of space was redirected from conquering distant planets to providing a better understanding of the human environment. Artificial satellites provide data pertaining to geographic formations, oceanic and atmospheric movements, and worldwide communications. The frequency of U.S. spaceflights in the 1960s and ’70s led to the development of a reusable, low-orbital-altitude space shuttle. Known officially as the Space Transportation System, the shuttle has made numerous flights since its initial launch on April 12, 1981. It has been used for both military and commercial purposes (e.g., deployment of communications satellites).

Aerospace engineering functions

In most countries, governments are the aerospace industry’s largest customers, and most engineers work on the design of military vehicles. The largest demand for aerospace engineers comes from the transport and fighter aircraft, missile, spacecraft, and general aviation industries. The typical aerospace engineer holds a bachelor’s degree, but there are many engineers holding master’s or doctorate degrees (or their equivalents) in various disciplines associated with aerospace-vehicle design, development, and testing.

The U.S. National Aeronautics and Space Administration (NASA) is a governmental organization that employs many engineers for research, development, testing, and procurement of military vehicles. Government agencies award and monitor industrial contracts ranging from engineering problem studies to design and fabrication of hardware. Universities receive limited funding, primarily for analytical research. Some of the larger institutions, however, are developing or expanding flight-research facilities and increasing faculty members in an effort to increase productivity in both research and testing.

The design of a flight vehicle is a complex and time-consuming procedure requiring the integration of many engineering technologies. Supporting teams are formed to provide expertise in these technologies, resulting in a completed design that is the best compromise of all the engineering disciplines. Usually the support teams are supervised by a project engineer or chief designer for technical guidance and by a program manager responsible for program budgets and schedules. Because of the ever-increasing requirement for advanced technology and the high cost and high risk associated with complex flight vehicles, many research and development programs are canceled before completion.

The design process can be dissected into five phases and is the same for most aerospace products. Phase one is a marketing analysis to determine customer specifications or requirements. Aerospace engineers are employed to examine technical, operational, or financial problems. The customer’s requirements are established and then passed on to the conceptual design team for the second phase.

The conceptual design team generally consists of aerospace engineers, who make the first sketch attempt to determine the vehicle’s size and configuration. Preliminary estimates of the vehicle’s performance, weight, and propulsion systems are made. Performance parameters include range, speed, drag, power required, payload, and takeoff and landing distances. Parametric trade studies are conducted to optimize the design, but configuration details usually change. This phase may take from a few months to years for major projects.

Phase three is the preliminary design phase. The optimized vehicle design from phase two is used as the starting point. Aerospace engineers perform computer analyses on the configuration; then wind-tunnel models are built and tested. Flight control engineers study dynamic stability and control problems. Propulsion groups supply data necessary for engine selection. Interactions between the engine inlet and vehicle frame are studied. Civil, mechanical, and aerospace engineers analyze the bending loads, stresses, and deflections on the wing, airframe, and other components. Material science engineers aid in selecting low-weight, high-strength materials and may conduct aeroelastic and fatigue tests. Weight engineers make detailed estimates of individual component weights. As certain parameters drive the vehicle design, the preliminary designers are often in close contact with both the conceptual designers and the marketing analysts. The time involved in the preliminary design phase depends on the complexity of the problem but usually takes from six to 24 months.

Phase four, the detailed design phase, involves construction of a prototype. Mechanical engineers, technicians, and draftsmen help lay out the drawings necessary to construct each component. Full-scale mock-ups are built of cardboard, wood, or other inexpensive materials to aid in the subsystem layout. Subsystem components are built and bench-tested, and additional wind-tunnel testing is performed. This phase takes from one to three years.

The final phase concerns flight-testing the prototype. Engineers and test pilots work together to assure that the vehicle is safe and performs as expected. If the prototype is a commercial transport aircraft, the vehicle must meet the requirements specified by government organizations such as the Federal Aviation Administration in the United States and the Civil Aviation Authority in the United Kingdom. Prototype testing is usually completed in one year but can take much longer because of unforeseen contingencies. The time required from the perception of a customer’s needs to delivery of the product can be as long as 10 to 15 years depending on the complexity of the design, the political climate, and the availability of funding.

High-speed computers have now enabled complex aerospace engineering problems to be analyzed rapidly. More extensive computer programs, many written by aerospace engineers, are being formulated to aid the engineer in designing new configurations.

Branches of aerospace engineering

The aerospace engineer is armed with an extensive background suitable for employment in most positions traditionally occupied by mechanical engineers as well as limited positions in the other various engineering disciplines. The transportation, construction, communication, and energy industries provide the most opportunities for non-aerospace applications.

Because land and sea vehicles are designed for optimum speed and efficiency, the aerospace engineer has become a prominent member of the design teams. Because up to half of the power required to propel a vehicle is due to the resistance of the air, the configuration design of low-drag automobiles, trains, and boats offers better speed and fuel economy. The presence of the aerospace engineer in the automobile industry is evident from the streamlined shapes of cars and trucks that evolved during the late 20th century, at a time when gasoline prices were escalating and the aerospace industry was in a lull. Airline companies employ engineers as performance analysts, crash investigators, and consultants. The Federal Aviation Administration makes use of the technical expertise of the aerospace engineer in various capacities.

The construction of large towers, buildings, and bridges requires predictions of aerodynamic forces and the creation of an optimum design to minimize these forces. The consideration of aerodynamic forces of flat surfaces such as the side of a building or superstructure is not new. In 1910 Alexandre-Gustave Eiffel achieved remarkable experimental results measuring the wind resistance of a flat plate, using the Eiffel Tower as a test platform.

Many companies benefit not from the advanced hardware developments of aerospace technology but by the understanding and application of aerospace methodology. Companies engaged in satellite communications require an understanding of orbital mechanics, trajectories, acceleration forces, and aerodynamic heating and an overall knowledge of the spacecraft industry. Advanced aerodynamic design of airfoils and rotor systems is applied in an effort to improve the efficiency of propellers, windmills, and turbine engines. The impact of aerospace technology has trickled down to many companies engaged in the research and development of flight simulation, automatic controls, materials, dynamics, robotics, medicine, and other high-technology fields.